There are a few too many factors that we don't know to give you all the proper specs. We can give you general information, but you need specifics. Some of the things we don't know: What kind of machine work was done to the block in preparation for rebuild? What kind of parts are we building with- stock, cheap aftermarket or quality race parts? If stock rods, were they reconditioned? Was the factory crank ground & polished? What kind of bearings are you using? What application will this motor be used for: N/A, nitrous, boost, daily driver? How many rpms will this motor need to turn: 5500, 6250, 7500?
Some precision measuring tools that you will need: bore micrometer, outside micrometer, feeler guages & a rod vise.
I'd recommend investing in a few books. No matter what you read on internet forums, it's always nice to have it in print when you go to do the work.
I'd suggest these 2 for starters: How to Rebuild Small Block Fords
& the Engine Builder's Handbook
. both of these are published by HP Books.
I'll try to get you started. Clean the backside of all your bearings with some 2+2. Assemble the rod bearings in the rods w/caps fingertight. Hold the rods with the rod vise and torque the caps. Remove the rods from the vice and measure the inside diameter of the bearings using the bore mic. Take measurements at 3-4 different spots around the bearing. Do this at each edge and around the center to verify that the bearing is 'true'. Write down your measurement for each rod.
Now using your outside mic, measure the rod journals on the crankshaft. Again, measuring at each edge and the center, 3-4 different spots around the journal. Write down these measurements. It'll help if you keep your rod measurements in order and then you can put the journal measurements write down along side. The difference in the diameter of the rod bearings and the rod journals is your clearance. I don't know what the specs are for what you're building. Probably somewhere in the range of .003"-.006".
You can use the same process for clearancing the main bearings. And the specs for those should be about the same. They could be more, but the most likely will not be less than .003" unless you're building a serious performance motor.
I know you're on a tight budget, but those books I mentioned will be invaluable to you now & in the future. Both of these books are available from Summit: Book 1
& Book 2
or checkout your local bookstore.
BTW, where are you located?
Please forgive me for any technical inaccuracies, it's 4:00am and I still have 3 more hours to go.